refactor(language-service): add generic decorator property verifications (#32252)

This PR makes finding class declarations properties in decorators are
applied to more generic to all properties that may be in a decorator,
and adds helper methods enabling getting the property assignment of a
property value and verifying that a property assignment is actually in a
decorator applied to a class.

This is done so that it will be easier to provide Angular definitions
for decorator properties moving forward. Most immediately, this will
provide decorator class verification for #32238.

PR Close #32252

packages/language-service/test/template_spec.ts

@@ -7,7 +7,7 @@
  */
 
 import * as ts from 'typescript';
-import {getClassDeclFromTemplateNode} from '../src/template';
+import {getClassDeclFromDecoratorProp} from '../src/template';
 import {toh} from './test_data';
 import {MockTypescriptHost} from './test_utils';
 
@@ -22,7 +22,10 @@ describe('getClassDeclFromTemplateNode', () => {
         class MyComponent {}`,
         ts.ScriptTarget.ES2015, true /* setParentNodes */);
     function visit(node: ts.Node): ts.ClassDeclaration|undefined {
-      return getClassDeclFromTemplateNode(node) || node.forEachChild(visit);
+      if (ts.isPropertyAssignment(node)) {
+        return getClassDeclFromDecoratorProp(node);
+      }
+      return node.forEachChild(visit);
     }
     const classDecl = sourceFile.forEachChild(visit);
     expect(classDecl).toBeTruthy();
@@ -37,9 +40,8 @@ describe('getClassDeclFromTemplateNode', () => {
     const sourceFile = tsLS.getProgram() !.getSourceFile('/app/app.component.ts');
     expect(sourceFile).toBeTruthy();
     const classDecl = sourceFile !.forEachChild(function visit(node): ts.Node | undefined {
-      const candidate = getClassDeclFromTemplateNode(node);
-      if (candidate) {
-        return candidate;
+      if (ts.isPropertyAssignment(node)) {
+        return getClassDeclFromDecoratorProp(node);
       }
       return node.forEachChild(visit);
     });